Indicate vertex-centric index usage in profiler result

[li-boxuan]

Closes #898, #2283

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[codecov-io]

Codecov Report

Merging #2360 (18cc6b0) into master (6fb94b8) will increase coverage by 0.00%.
The diff coverage is 90.00%.

@@            Coverage Diff            @@
##             master    #2360   +/-   ##
=========================================
  Coverage     70.34%   70.35%           
- Complexity     7725     7731    +6     
=========================================
  Files           681      681           
  Lines         29865    29873    +8     
  Branches       4824     4825    +1     
=========================================
+ Hits          21010    21016    +6     
- Misses         6335     6339    +4     
+ Partials       2520     2518    -2     

Impacted Files	Coverage Δ	Complexity Δ
...raph/diskstorage/keycolumnvalue/KeySliceQuery.java	72.22% <0.00%> (ø)	9.00 <0.00> (ø)
...usgraph/graphdb/query/graph/GraphCentricQuery.java	66.66% <ø> (ø)	16.00 <0.00> (ø)
...anusgraph/graphdb/query/profile/QueryProfiler.java	89.65% <ø> (ø)	10.00 <0.00> (ø)
...usgraph/diskstorage/keycolumnvalue/SliceQuery.java	79.16% <100.00%> (+4.16%)	27.00 <3.00> (+3.00)
...rg/janusgraph/graphdb/database/EdgeSerializer.java	80.60% <100.00%> (+0.38%)	79.00 <0.00> (+1.00)
...usgraph/diskstorage/PermanentBackendException.java	66.66% <0.00%> (-33.34%)	2.00% <0.00%> (-1.00%)
...a/org/janusgraph/util/system/BackgroundThread.java	66.66% <0.00%> (-4.77%)	6.00% <0.00%> (-2.00%)
...ph/diskstorage/hbase/HBaseKeyColumnValueStore.java	76.22% <0.00%> (-2.46%)	20.00% <0.00%> (ø%)
...a/org/janusgraph/diskstorage/log/kcvs/KCVSLog.java	84.49% <0.00%> (-0.31%)	44.00% <0.00%> (+1.00%)	⬇️
... and 4 more

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[farodin91]

LGTM!